Apparatus for bracing vertebrae

ABSTRACT

An apparatus for bracing a plurality of vertebrae of the human spine has at least two pedicle screws, each having an annular head with an opening therewithin and including a slot therewithin. Each slot extends into the corresponding opening and includes internal threaded portions. A securing screw to be screwed in each slot is provided. A relatively stiff threaded rod is also provided and is to be inserted into the opening in the head of each of the pedicle screws and to be secured by the securing screws. Adjusting nuts are screwed on the rod and at least one cooperates with each head.

This application is a continuation of U.S. Ser. No. 08/839,540, filedApr. 14, 1997 now U.S. Pat. No. 6,090,110 which is a continuation ofU.S. Ser. No. 08/384,639, filed Feb. 6, 1995, abandoned which is acontinuation of U.S. Ser. No. 08/025,196, filed Mar. 2, 1993 abandoned.

The present invention relates to an apparatus for bracing a plurality ofvertebrae of the human spine.

Known supporting means operate with so-called lamina hooks which aredisposed on a threaded rod. A compressing means is disclosed in Britishpatent 2 131 300. A distracting means is disclosed in U.S. Pat. No. 4383 438. The threaded rod bridges a plurality of vertebras and is notsuited to act on vertebras which are disposed between the lamina hooks.The thread of the rod is used to fix the lamina hooks. Before using thesupporting means a distraction or, respectively, compression has to beprovided by means of an additional device.

German 90 06 646 U1 discloses an apparatus in which a lamina hook isreplaced by a clamp-shaped holding member having a pair of legs of whichone can be bent with respect to the other. Thereby the giapophysis ofthe vertebras may be used as anchoring points for the compressing anddistracting apparatus.

German 88 02 112 U1 teaches a supporting device for the human spine,according to which the so-called pedicel screws are screwed in thepedicel body of the vertebras. The pedicle screws cooperate withtensioning means which bridge across one or more vertebrae to introduceforces between the vertebrae. The known device affords a primarystabilization of the vertebrae with respect to all degrees of freedom.However, when a number of vertebrae of a non-traumatic spine forexample, are to be repositioned, separate means necessary to perform thereposition before the known supporting device may be effectively used.

WO 91/01691 discloses an apparatus for bracing vertebras of the humanspine, comprising pedicle screws having slotted heads to receive a rod.The legs of the slotted screw heads include an outer thread on which anut is screwed which contacts the rod to fix a predetermined position.

EP 0 443 892 discloses a similar device comprising a pedicle screw, theslotted head thereof including internal threaded portions for receivinga fixing screw which is brought into engagement with a serrated orsimilarly roughened rod to fix the relative position of the rod and theindividual pedicel screw. A ring disposed around the head of a pediclescrew is provided so that the legs of the screw head do not spread apartwhile fixing the rod, as otherwise the engagement between the fixingscrew and the screw head may be lost. A similar apparatus is disclosedin WO 90/09156.

Again, the devices last mentioned require separate means forrepositioning, thus being suited to maintain a repositioned condition,but not suited to perform repositioning.

It is an object of the present invention to provide an apparatus whichis suited to reposition the vertebrae of the human spine as well as tosupport the vertebrae in the repositioned position thereafter.

The objects are solved by the apparatus of the invention.

SUMMARY OF THE INVENTION

According to the invention, the apparatus uses a threaded rod (i.e., adistracting rod) in combination with lamina hooks. The thread of therod, however, is not only used to fix the pedicle screws, but further isused to reposition the vertebrae in that an adjusting nut sitting on thethreaded rod is turned with respect to the head of the pedicle screw andthus the vertebra has obtained the desired position. By means of theapparatus according to the invention a spine portion is not onlydistracted or compressed, but individual vertebrae can be effectivelypositioned with respect to each other. To this end the threaded rod isdesigned to be relatively stiff and has a diameter between 7 to 8 mm,for example. On the other hand the rod must be bent to be implantedclose to the spine along a bent spine portion. This is facilitated bythe design of the pedicle screw heads having slots for receiving thethreaded rod. To hold the rod in the slot, a securing screw is provided.Whereas the screw in the pedicle screw head according to EP 0 443 892,for example, axially fixes the rod, the securing screw of the presentinvention is merely used to prevent a deflection of the rod out of thereceiving slot.

After resetting, the adjusting nut must be fixed on the threaded rod.This can be obtained by means of a suitable counter-nut. Still further,it is possible, to provide the adjusting nut and the front faces of thepedicle screw head with a rotary safety means in form of a toothing oranother irregularity cooperating in a clamping fashion. In both casesthe nuts are merely fixed by a frictional force. According to a furtherembodiment of the invention, however, the head of the pedicle screw hasa width smaller than the diameter of the securing screw, whereas atleast one front face of the adjusting nut has a recess cooperating withthe securing screw. Preferably, the adjusting nut includes a pluralityof peripherally spaced indentations, wherein the final rotary positionof the nut is such that the securing screw cooperates with theindentation. This affords a positive locking of the adjusting nutresulting in a precise rotary locking which cannot be loosened.

The pedicel screws must take up relatively large forces. There is thedanger that a pedicel screw breaks out of the bone, primarily when theavailable bony substance does not provide a sufficiently rigid seat inthe vertebra. According to an embodiment of the invention, a mountingstrap is attached to the shaft of the pedicel screw laterally extendingtherefrom, which strap includes an opening for receiving a spongiosescrew. The strap has, for example, a pair of openings, wherein oneopening receives the shaft of the pedicel screw, while the other openingdisposed at the other end of the strap, for example, receives aspongiose screw which is screwed into the vertebra. In this manner, thepedicel screw is laterally stabilized and can receive substantialforces. According to an alternate embodiment of the invention, amounting strap may be provided to the shaft of the pedicel screwextending therefrom, which strap has a blade or the like to be mountedin the vertebra. The blade is preferably integral with the strap. Theblade is beaten into the vertebra wherein the strap may additionallyinclude a hole for receiving a spongiose screw which is screwed into thevertebra. In some cases, a vertebra is displaced with respect to theadjacent vertebra. When the pedicel screw is completely screwed in, itcannot be connected any more with the threaded rod. To accomplish aconnection, the pedicel screw is partly screwed into the vertebra bone.According to an embodiment of the invention, the head of the pediclescrew is then rotatably mounted on the screw shaft so that by rotatingthe shaft the vertebra can be pulled up to the threaded rod forresetting. Preferably the shaft includes tool engaging faces adjacentthe head to rotate the shaft of the screw in the desired manner.

In case of very specially displaced individual vertebrae, not even thefeatures referred to above are sufficient. According to a furtherembodiment of the invention, the upper end of the pedicle screw shaft isball-shaped, while the pedicel screw head is defined by a ball-engagingcage including a slot for the rod. The cage can be arbitrarilypositioned with respect to the shaft of the screw, but can exert atensioning force to the screw shaft when being screwed in the vertebra.According to both embodiments just referred to, the threaded rod isinserted through a slot of the pedicel screw head, wherein a securingscrew referred to several times prevents the rod from sliding out of theslot. Alternatively a closed passage may be provided in the head of thepedicle screw as it is known per se.

Instead of or in addition to the pedicle screw the apparatus of thepresent invention provides a hook cooperating with a lamina of avertebra. Those lamina hooks are generally known. According to theinvention, however, the lamina hook is provided with a slotted receivingportion to insert the threaded rod. The slot has threaded portions againto secure the rod in the receiving slot.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described by way ofexample with reference to the accompanying drawing.

FIG. 1 schematically shows an apparatus according to the invention to beused as a distracting system,

FIG. 2 schematically shows an apparatus according to the invention usedas a compressing system,

FIG. 3 shows a pedicel screw for the apparatuses according to FIGS. 1and 2,

FIG. 4 shows the pedicel screw of FIG. 3 cooperating with a threadedrod,

FIG. 5 schematically shows a side view of a further embodiment of apedicel screw for the apparatuses of FIG. 1 and 2,

FIG. 6 shows a side view of the pedicel screw of FIG. 5 rotated about90°,

FIG. 7 shows a plain view of the pedicel screw of FIG. 5,

FIG. 8 shows a side view of an adjusting nut of the apparatus of FIGS. 1and 2,

FIG. 9 shows a stabilizing strap for the apparatus of FIGS. 1 and 2,

FIG. 10 shows a further embodiment of a stabilizing strap of theapparatus of FIG. 1 and 2,

FIG. 11 shows a section of a lamina hook for the apparatus of FIGS. 1and 2,

FIG. 12 shows a plain view of the hook of FIG. 11,

FIG. 13 shows a side view of a further embodiment of a pedicle screw foran apparatus according to the invention,

FIG. 14 shows a side view of the pedicle screw of FIG. 13 turned about90°,

FIG. 15 shows a side view partly in section of a further embodiment of apedicle screw for an apparatus according to the invention and

FIG. 16 shows a side view of the pedicle screw of FIG. 15 turned around90°.

FIG. 1 shows a bent spine portion 10 wherein the individual vertebrasshall be distracted by means of a distracting system 12. The systemcomprises a relatively stiff threaded rod 14 having a diameter of 6 to 9mm, preferably 7 to 8 mm. It cooperates with an individual pedicel screw16 screwed in the vertebras. Details of the screws are shown in thefollowing figures. The threaded rod 14 is received in slots of thepedicel screw heads 16 and a plurality of adjusting nuts 18 is disposedon the rod 14, at least one nut each for a pedicel screw 16. Stabilizinglatches 20 cooperate with the pedicel screws, which latches include ahole 22 in a distance from the pedicle screw to receive a spongise screwscrewed in the vertebra. By means of the adjusting nut 18 a pedicelscrew screwed in the vertebra may be displaced relative to the rod 14and thus with respect to the vertebra receiving the screw. By means ofthe adjusting nuts 18 the vertebrae of the portion 10 may be thusadjusted to accomplish a distraction.

The spine portion 30 shown in FIG. 2 comprises a compressing meansincluding components identical with those shown in the system 12 so thatidentical components carry identical reference numerals. To reduce thebending of the spine portion 30 a tension force must be exerted on thevertebras to straighten the bent threaded rod 14. This is accomplishedby adjusting the individual pedicle screws 16 as described in FIG. 1. Inthe following the components of the system referred to are described inmore detail.

FIG. 3 shows a pedicel screw 16 a having a shaft 32 and an annular head34. The head 34 includes a slot 36 in which the rod 14 is inserted. Asecuring screw 38 a cooperating with threaded portions in the slot 36holds the threaded rod 14 in the slot 36. FIG. 4 shows adjusting nuts 18a located on either side of the head 34 to displace the screw 16 a alongthe rod 14.

In the embodiment of FIGS. 5 and 6 the pedicel screw 16 b has arelatively narrow head 34 b so that the securing screw 38 b laterallyprojects. This is shown by the dashed line in FIG. 7. when an adjustingnut 40 according to FIG. 8 is used, which nut is provided withindentations 42 on the opposite front faces thereof, the nut 40 can besecured to the rod 14 when an indentation 42 of the screw 38 bcooperates with the adjusting nut 38 b.

FIG. 9 shows a mounting strap. The plate-shaped strap 20 includes afirst hole 44 receiving the shaft of a pedidel screw. A second hole 22receives a spongiose screw as mentioned before.

FIG. 10 shows an alternate embodiment 20 a of a stabilizing latch, againcomprising a hole 44 a for a pedicle screw and a hole 22 a locatedsubstantially in the center for receiving a spongiose screw. FIG. 10further shows a blade 46 integrally shaped on the end opposite the hole44 a which blade is driven home in the vertebra.

FIGS. 11 and 12 show a lamina hook 50 comprising a hook portion 52 and areceiving portion 54 including a slot 56. The slot 56 receives athreaded rod such as the rod 14 shown in FIGS. 1 and 2. Threadedportions as indicated at 58 in FIG. 11 are provided inside the slot 56to receive a securing screw not shown to hold the rod in the slot 56.The position of the rod in the slot 56 is determined by the position ofthe securing screw not shown, wherein a relative position between thehook 50 and the rod is possible to a limited extent.

FIGS. 13 and 14 show a pedicel screw 16 c comprising a shaft 32 c and anannularly closed head 34 b through which a rod 14 extends. A fixingscrew 60 in the head 34 b is used to fix the threaded rod 14. However,adjusting nuts may be used as mentioned before. According to theembodiment of FIGS. 13, 14 the shaft 32 c is rotatably mounted in thehead 34 b. Accordingly, a circular blind bore 62 holds a ring 64cooperating with an annular groove 66 in the shaft 32. Tool faces 68facilitate a rotation of the shaft 32 c relative to the head 34 c whenit fixedly sits on the rod 14 for example. It should be understood thatthe head 34 c may provide a slot as shown in FIGS. 3 to 7 for example.

In the embodiment of FIGS. 15 and 16 a pedicel screw 16 d is providedcomprising a shaft 32 d which upper end is formed as a ball 70. A cage72 cooperates with the ball, the cage further having a passage 74 toreceive a threaded rod 14. Furthermore, the cage 72 has threadedportions to receive a securing screw 38 d. This allows to rotate theshaft 32, wherein tool faces 68 d are provided. Furthermore, the shaft32 d may be pivoted relative to the cage 72 in a limited angle.

What is claimed is:
 1. An assembly for setting a spine comprising ananchoring element, including a shaft portion to be attached to avertebrae, a first end of said anchoring element being formed by a ball;a cage which has an aperture at a first end through which said shaftportion of said anchoring element extends, wherein the diameter of saidshaft portion adjacent said aperture is smaller than that of saidaperture, said cage including a partially ball shaped surface forengaging said ball shaped first end of said anchoring element, said cageincluding a passageway opened to a second end of said cage opposite tosaid aperture for receiving a rod and a securing screw to be screwed inan axial direction onto a thread provided at said second end of saidcage in the area of said receiving slot to urge said rod received insaid receiving passageway into contact with said first end of saidanchoring element to secure said assembly.
 2. The assembly as set forthin claim 1 wherein said shaft includes a drive element.
 3. The assemblyas set forth in claim 1 wherein said anchoring element is threaded.
 4. Apedicle screw assembly, comprising: a pedicle screw having a ball shapedhead and a threaded shaft; a cage having a longitudinal axis and aninner partially ball shaped portion with an aperture at a first endsized to allow said threaded shaft to pass through while capturing saidhead against said partially ball-shaped surface, said cage having apassageway formed at an open second end thereof opposite first end andan axially extending threaded portion adjacent said passageway; a rodextending through said passageway; and a securing screw operativelyengageable with said thread for axial movement within said cage intocontact with said rod causing said rod to act on said first end of saidanchoring element to secure said assembly.
 5. A pedicle screw assemblyfor connecting a pedicle screw to a rod comprising: a pedicle screwhaving a threaded shaft and a ball-shaped head; a hollow cage having acentral longitudinal axis, a first end with a partially ball shapedinner portion for engaging said ball shaped head and an aperturecentered around said axis for receiving said shaft, said cage having asecond threaded open end centered around said axis including apassageway extending in a direction transverse to said longitudinal axisfor receiving the rod; a securing screw for engaging said threads formovement along said axis into contact with the rod to secure said rodagainst said ball shaped head.